WO2012117261A1 - Methods and apparatus for detection of fluid interface fluctuations - Google Patents

Methods and apparatus for detection of fluid interface fluctuations Download PDF

Info

Publication number
WO2012117261A1
WO2012117261A1 PCT/GB2012/050489 GB2012050489W WO2012117261A1 WO 2012117261 A1 WO2012117261 A1 WO 2012117261A1 GB 2012050489 W GB2012050489 W GB 2012050489W WO 2012117261 A1 WO2012117261 A1 WO 2012117261A1
Authority
WO
WIPO (PCT)
Prior art keywords
acoustic
phase shift
receiver
signals
acoustic signals
Prior art date
Application number
PCT/GB2012/050489
Other languages
French (fr)
Inventor
Kirill Horoshenkov
Andrew Nichols
Original Assignee
University Of Bradford
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University Of Bradford filed Critical University Of Bradford
Priority to US14/002,569 priority Critical patent/US20130333483A1/en
Priority to EP12715702.2A priority patent/EP2681520A1/en
Publication of WO2012117261A1 publication Critical patent/WO2012117261A1/en

Links

Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/66Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/28Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/296Acoustic waves
    • G01F23/2962Measuring transit time of reflected waves
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01FMEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/80Arrangements for signal processing
    • G01F23/802Particular electronic circuits for digital processing equipment
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06Systems determining the position data of a target
    • G01S15/08Systems for measuring distance only
    • G01S15/32Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G01S15/36Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and the contemporaneously transmitted signal
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52004Means for monitoring or calibrating
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/54Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 with receivers spaced apart

Definitions

  • the present invention relates generally to acoustic technologies, and more particularly to methods and apparatus for detection of fluctuations in an interface between two fluids.
  • the invention further relates to processors and computer program products adapted for use in such methods.
  • An example of an interface between two fluids is the free surface of a liquid (first fluid) under a gaseous atmosphere (second fluid).
  • the liquid may be relatively static, with surface fluctuations caused by wind, for example.
  • the liquid may be flowing in a conduit or channel with surface fluctuations (waves) caused additionally by turbulence. It is important to monitor flow conditions of free-surface flow in a number of applications, such as river flood monitoring, flow control in water and waste treatment, petrochemical and food processing plants.
  • ultrasonic devices To gauge the relative position of a water surface in order to calculate depth. These operate with airborne acoustic signals to measure the surface height in a static or average way, for example to measure the fill state of a storage tank, or the state of a tide.
  • Airborne Doppler techniques are known to be used to quantify the horizontal component of surface velocity of water flows.
  • Other airborne time-of-flight acoustic range finding techniques have been used to measure the static level of water by emitting short pulses (e.g. N. A. Bolton, Liquid Level Indication System, US Patent 3,184,969, June 10, 1963; S. D. Lenz, R.
  • Various embodiments of the present invention provide non-invasive methods and systems for detection of fluctuations in fluid interfaces such as free surfaces of flowing liquid, thereby to address one or more of the drawbacks of the aforementioned prior art.
  • a method for measuring dynamic characteristics of an interface between two fluids comprising:
  • processing the detected signals to measure phase shift between the sent and received acoustic signals, the measured phase shift varying over time, and using the variations in phase shift to indicate fluctuations over time in the position of the fluid interface in the target area.
  • the target area can be designed to have a size smaller than a dominant spatial scale of said localised fluctuations at the interface.
  • said two fluids are a gas (which includes a vapour) and a liquid, said interface being a free surface of the liquid, the acoustic source and receiver being positioned above the liquid surface, the variations in phase shift being used indicate fluctuations over time in the height of the liquid surface.
  • the liquid may be flowing in a natural or man-made channel or conduit.
  • the method further comprises deriving from the measured variations in phase shift a characteristic of the flowing liquid such as: surface roughness, wave height, flow velocity, volumetric flow rate, shear stress, sediment transport.
  • the sent acoustic signals may comprise a harmonic sine wave.
  • Said processing step may comprise comparing phases of the sent and received signals over several cycles of said sine wave to obtain a measurement of said phase shift at a given time.
  • the phase shift may be is determined on the basis of Hilbert transforms of data representing the sent and detected acoustic signals.
  • the method may further comprise arranging a plurality of acoustic receivers at different positions relative to the acoustic source so as to receive acoustic signals that have reflected simultaneously from different target areas on the fluid interface and processing the received acoustic signals so as to measure a time-varying phase shift corresponding to each of said target areas.
  • the plurality of receivers may be spaced to allow different separation distances between different pairs of the receivers.
  • the plurality of receivers may be spaced in two dimensions so that said different target areas are spaced in two dimensions over the fluid interface.
  • the method may further comprise measuring a temporal lag between fluctuations measured for different target areas (i.e. by different receivers).
  • a flow velocity may be derived from the temporal lag and from knowing the distance between the target areas in a direction fo fluid flow.
  • the method may further comprise determining a wave height at the target area on the basis of the measured variations in phase shift, a known separation of the acoustic source and receiver and a known receiver height relative to said interface.
  • Said known receiver height may be obtained by measuring a time of flight of an acoustic signal sent from said acoustic source, and received by said acoustic receiver following reflection from the interface.
  • a method for detecting liquid surface fluctuations comprises: sending acoustic signals from a first known point to a point on a liquid surface; receiving said acoustic signals at a second known point after reflection from the liquid surface; processing the detected signals periodically to monitor variations in phase shift between the sent and received acoustic signals, and using the variations in phase shift to indicate fluctuations in the height of the liquid surface at the point.
  • a system for detecting liquid surface fluctuations comprises: a signal emission module operable to send acoustic signals from a first known point to a point on a liquid surface; a signal detection module operable to receive said acoustic signals at a second known point after reflection from the liquid surface; and a processing module operable to process the detected signals periodically to monitor variations in phase shift between the sent and received airborne acoustic signals, and using the variations in phase shift to indicate fluctuations in the height of the liquid surface at the point.
  • a processor operable to process sent and received acoustic signals of the above method for detecting fluid interface liquid surface fluctuations.
  • a computer-readable medium including instructions which when executed by a computer can process sent and received acoustic signals of the above method for detecting liquid surface fluctuations.
  • Figure 1 is a schematic side view of an exemplary system for detecting liquid surface fluctuation according to one embodiment of the present invention.
  • Figure 2 shows an example of a signal detection module having a plurality of receivers to receive acoustic signals in (a) schematic side view and (b) and (c) plan views of different variants.
  • Figure 3 is a flowchart of an exemplary method for detecting liquid surface fluctuation according to one embodiment of the present invention.
  • Figure 4 is a flowchart of an exemplary method for detecting liquid surface fluctuation according to another embodiment of the present invention.
  • Figure 5 is a flowchart of an exemplary method for determining the height of signal detection module above the liquid surface, usable in the methods of Figures 3 and 4.
  • Figure 6 is an explanatory illustration of path lengths of two acoustic signals travelling from the signal emission module 110 to the signal detection module 120.
  • Figure 7 is a set of graphs showing the water surface fluctuation Y over time X as measured by a conventional conductance probe and by an acoustic probe forming an embodiment of the present invention.
  • Figure 8 is a set of graphs demonstrating the relationship of the measured water surface RMS surface roughness ⁇ to (a) mean flow velocity v and (b) hydraulic roughness k s .
  • Figure 9 is a graph showing correlation coefficients varying with receiver separation.
  • Figure 10 demonstrates a relationship between volumetric flow rate F and measured water surface roughness.
  • Figure 11 demonstrates relationships between depth of flowing water and measured water surface roughness, for various bed gradients.
  • Figure 12 demonstrates a relationship between flow surface characteristic period P and shear stress ⁇ at a channel bed.
  • FIG. 1 shows an exemplary system 100 for detecting liquid surface fluctuation in accordance with various embodiments presented therein.
  • System 100 comprises a signal emission module (emitter for short) 110, a signal detection module (receiver for short) 120 and a processing module 130.
  • System 100 can be deployed to detect fluctuations in the height at a point 162 on a liquid surface 160.
  • the fluctuation over time may be represented by as a wave height at the point 162.
  • point 162 will not be an infinitely small point, but rather a target area.
  • the size of the target area can be made small relative to the surface fluctuations that are to be monitored, as discussed further below.
  • System 100 may be positioned above the liquid surface 160 or below the liquid surface 160.
  • system 100 is operable to perform airborne acoustic inspection of hydraulic flow in shallow water channels, rivers, partly filled pipes and other unpressurised conduits.
  • a flow with velocity v is indicated schematically by an arrow.
  • the modules 110 and 120 may be mounted beneath a bridge over a river, in the roof of a conduit, or on their own platform, according to convenience.
  • the fluctuations caused by turbulence and other mechanisms in such a real-world system will be more complex and three-dimensional than the simple wave shape shown in Figure 1. Also, the height of the fluctuations is greatly exaggerated in Figure 1, relative to the scale of the apparatus as a whole.
  • Signal emission module 110 comprises a signal generator and a transducer operable as an acoustic source to emit one or more airborne acoustic signals.
  • Receiver 120 comprises a microphone or other transducer operable as an acoustic receiver to detect the one or more acoustic signals after reflection from a small target area the liquid surface.
  • Processing module 130 is capable of data communication with emitter 110 or receiver 120 via a cable or wirelessly.
  • wireless data communication may be a short range wireless communication via a short distance data transmission technology standard such as Bluetooth (RTM).
  • Processing module 130 may be a mobile personal computer, a handheld device or other computing device.
  • emitter 110 is mounted at an angle between ten and eighty degrees to the horizontal, which may, for example, be approximately forty-five degrees.
  • the emitter 110 may include an array of acoustic transducers, each of which is operable to emit an acoustic signal. In that case, controlling the relative phases of the emitted signals allows the direction and directivity of the acoustic signal to be controlled. Actively steering the beam is an option, for example to adjust for different surface heights, though it would add to cost and may reduce robustness of a device. Alternatively, one can design the geometry of the emitter-receiver arrangement such that the receiver is within the reflected beam for all reasonable flow depths, and use active steering when this is not possible.
  • processing module 130 controls emitter 110 to emit acoustic signals 140 over an extended period of time
  • Processing module 130 triggers receiver 120 to receive airborne acoustic signals 150 reflecting back from surface 160 and processes the received signals on a continuous or pseudo-continuous basis.
  • the signals follow different paths as the surface moves over time.
  • the surface at different times may have different shapes illustrated by the solid and broken curves 160 and 160'.
  • the path of the acoustic signals may be as shown in the solid lines 140 & 150 at one time, and as shown by the broken lines 140' & 150' at another time.
  • the signal emission module (emitter) 110 in a simple embodiment emits a continuous ultrasonic sine wave at the resonant frequency of emitter 110 such as 45 kHz, and at an angle of, for example, 45 degrees to the horizontal.
  • the emitted acoustic signal may be configured to be a monochromatic sine wave at the resonant frequency of the transducer.
  • the wavelength [ ⁇ ) of the acoustic signal may be selected to be comparable with the maximum amplitude of the water surface roughness or greater than the root mean square of the water surface roughness height ( A ⁇ ⁇ ), and a continuous harmonic signal may be emitted.
  • Figure 2 (a) shows an embodiment of system 100 in which signal detection module 120 comprises a horizontal array of receivers 122a, 122b, 122c etc., such as microphones, spaced horizontally from emitter 110 with different distances Dl, D2, D3.
  • the array of microphones may be installed and mounted on the same horizontal axis as emitter 110 and at a distance in front of emitter 110 equal to twice the approximate height above liquid surface 160, where the incidence angle is 45 degrees.
  • the microphones can be arranged in the form of a vertical array to cover the same range of angles of incidence.
  • Each microphone 122a etc. will receive acoustic signals 150a etc. which have been reflected from a different area 162a, etc.
  • this insonified zone is determined by the distance to the liquid surface from the emitter transducer, the directivity of the acoustic signal (that is the ratio of the acoustic wavelength to the transducer dimension ⁇ I d ) and the incidence angle.
  • the dimensions of this zone should be chosen to be comparable to the correlation radius of the dynamic water surface roughness.
  • the distance between the transducer and the water surface is chosen to satisfy the far-field conditions, i.e. L a » 2d 2 1 ⁇ where L a is the reflected path length.
  • a target area on the surface from which a dominant acoustic signal is received at a particular receiver is designed to be small in relation to a dominant spatial scale of said localised fluctuations at the liquid surface.
  • the beam of sound projected can be is relatively directional, as already described. The amplitude of the emitted sound pressure thus strongly depends on the angle of incidence which is maximum in the direction of specular reflection to the receiver(s).
  • the area of the flow surface which carries key phase information about the water surface elevation is small by designing the system to exploit the Fresnel zone effect.
  • the acoustic wavelength is carefully selected to minimise the Fresnel zone dimensions.
  • the acoustic wavelength may be less than 15 cm, less than 10 cm for example.
  • the characteristic spatial period of the flow surface roughness is assumed to be large in comparison with the acoustic wavelength, so that any reflections from outside the Fresnel zone are deemed to be uncorrelated with the signal received through the angle of specular reflection.
  • the frequency of sound can be carefully selected to ensure that, and phase comparisons can incorporate a sufficient number of cycles to eliminate uncorrelated signal components.
  • a plurality of receivers allows for analysis of acoustic data reflected from different areas of the surface and allows for water surface roughness with different correlation radii to be analysed. Additionally, a plurality of receivers arranged along a horizontal axis allows for mean surface gradient deduction by measurement of reflected path-length from emitter 110 to each respective receiver of receiver 120. The distances Dl, D2, D3 etc. are chosen such that each possible paring of receivers give rise to a unique separation between them. For example, four microphones may have six possible parings. Each receiver has an associated channel to output its received signal to processing module 130.
  • the receivers 122a to 122c are shown spaced away from emitter 110 along a line parallel with the general flow direction of the liquid being monitored. They could be arranged transversely or obliquely to the flow direction if desired.
  • a larger number of receivers are arranged in a two-dimensional grid pattern, so as to measure at various points across the stream. A simply 'crosshairs' arrangement can be provided, as shown in solid lines, or a more elaborate array of receivers can be provided as indicated by the dotted receivers.
  • the emitter in these examples is shown to one side of the receiver array, but can be placed within it, for example at the centre of a crosshair or grid arrangement. Such an arrangement may be more compact.
  • the emitter in that case may point vertically, or may comprise a number of emitters inclined outward from vertical.
  • the received acoustic signals of course are reflected from a target point or area mid-way between the receiver and the source, as seen in the side view of Figure 2(a). Therefore the overall surface area sampled by the small target areas is half the size (in each dimension) of the array of receivers.
  • processing module 130 is triggered to acquire acoustic data in packets at a frequency high enough to capture surface fluctuation but low enough to conserve memory and processing power.
  • the triggering frequency depends on the nature of the surface fluctuations, which may for example be between lHz and 500Hz. In one embodiment, the triggering frequency is 100Hz and the number of acquired sinusoidal periods of data for each trigger is greater than 10.
  • the emitter 110 emits a continuous sine wave, whose phase and frequency are stable over the time period between sending and receiving acoustic signals from the liquid surface. In an alternative embodiment, the emitter 110 is triggered to emit signals only in packets, synchronised with the received packets.
  • the emitting and receiving modules must be synchronised so that the phase of the sent and received signals can be compared with suitable accuracy.
  • the sine wave may be continuously generated, so as to be available for comparison with the received signal, while its amplification and output to the emitting transducer is gated so that the acoustic signal is only emitted in packets.
  • the processing module 130 may be operable to acquire a packet (as an example, each packet may be 1ms) of acoustic data at each trigger from receiver 120 and determine a phase shift of each acoustic signal between the emitted signal and the received signal.
  • Processing module 130 is operable to sample the acoustic data at a frequency greater than the Nyquist frequency of twice the frequency of the emitted signal.
  • the sampling frequency may be at least ten times the emitted acoustic signal frequency and in one embodiment may be lMHz.
  • Processing module 130 may also be operable to band-pass filter each packet of acoustic data to isolate the transmission frequency of emitter 110, and to analyse each packet of acoustic data to extract the phase shift between the emitted and received signals.
  • processing module 130 is not limited by using a particular means of determining the phase shift between the emitted and received signals. Instead, processing module 130 is interpreted to cover any means which may be employed to determine a phase shift between the emitted and received signals.
  • processing module 130 is operable to average the phase shift measured and unwrapped at different points within the packet, to give a phase shift value for that packet.
  • the instantaneous phase of the received signal at each microphone is thereby known for each packet. Since the packet triggering frequency is known, a time can be associated with each phase measurement.
  • the processing module may be operable to provide a time series of phase shifts, from which phase variations representing surface fluctuations can be observed.
  • Figure 3 is a flowchart illustrating the general principle of detecting liquid surface fluctuation with reference to the components disclosed in system 100.
  • emitter 110 can send acoustic signals 140 and 150 towards the point 162 of the liquid surface 160 at a first time and a second time, respectively.
  • receiver 120 receives acoustic signals 140 and 150 reflecting back from the point 162 at a third time and a fourth time, respectively.
  • processor module 130 determines a first phase shift of the first acoustic signal and a second phase shift of the second acoustic signal.
  • the first phase shift indicates a time-dependent phase shift of the first acoustic signal between the first time and the third time.
  • the second phase shift indicates a time-dependent phase shift of the second acoustic signal between the second time and fourth time.
  • processor module 130 determines phase variation information on the basis of the first phase shift and the second phase shift. If the liquid surface 160 is stationary (or at least is at the same place when the two acoustic signals are reflected), the value of the first phase shift is same to the value of the second phase shift. Consequently, the value of the phase variation is zero and indicates that there is no fluctuation at point 162.
  • the phase variation is capable of indicating the surface fluctuations on an arbitrary scale and thus allowing emitter 110 and receiver 120 to be positioned anywhere above the air-water interface.
  • FIG. 4 is a flowchart of a method 300 comprising an embodiment of the invention based on the method 200 described above.
  • steps 310-340, and optionally further steps are repeated in a continuous loop, while surface fluctuations are to be measured.
  • emitter 110 emits acoustic signals in sine wave form. The signals may be emitted as a continuous sine wave or in discrete packets.
  • receiver 120 is triggered synchronously with the emitter and it receives a packet of acoustic data.
  • processing module 130 calculates Hilbert Transforms of the sent and received acoustic data.
  • processing module 130 determines the phase shift for each packet of acoustic data from the Hilbert Transforms. This is done by taking the natural logarithm of the ratio of the analytic signals, the imaginary part IM of this being the time dependent phase shift, ⁇ ( ⁇ ) , between the sent and received acoustic data: For each packet of acoustic data, the calculated phase shifts are averaged to give a single phase shift for that packet.
  • Processing module 130 can thus form a time series of phase fluctuations between + ⁇ and— ⁇ .
  • processing module 130 tracks the phase gradient and its sign of each phase fluctuation so that phase differences that exceed + ⁇ and - ⁇ can be extracted. These phase differences are associated with surface height fluctuations exceeding acoustic wavelength A .
  • the acoustic wavelength of the acoustic signal from the emitter 110 is 7.6 mm. Tracking phase differences greater than + ⁇ and— ⁇ is therefore important for tracking surface height fluctuations greater than a few millimetres. Processing routines, for example 'unwrapping' functions in Matlab, for example, are readily available to implement this function to follow the phase variations over a range greater than ⁇ ⁇ .
  • processing module 130 can obtain the height of receiver 120 above the liquid surface so that the arbitrarily scaled phase fluctuations so far calculated can be scaled as required. Where the height of the receiver 120 above the surface is unknown, the height may be obtained by processing module 130 in accordance with an exemplary method as described below. Figure 5 illustrates such a method.
  • emitter 110 sends an acoustic short pulse signal to the liquid surface 160.
  • receiver 120 receives the acoustic signal.
  • processing module 130 obtains the time for the acoustic signal travelling from emitter 110 to receiver 120.
  • processing module 130 calculates the reflected path length of the acoustic signal travelling from emitter 110 to receiver 120, using the known value for the speed of sound in air.
  • processing module 130 can use the distance and the reflected path length calculated at step 440 to calculate the height of receiver 120 above the liquid surface, using the Pythagoras theorem.
  • the measured height is used to calculate a scale factor for use in converting measured phase variations (measured by angle) into liquid surface height variations (measured in millimetres). Details of this calculation will be given below.
  • the spatial surface fluctuation Ah is calculated according to: where h is the height of receiver 120 above surface 160, D is the distance between emitter 110 and receiver 120, and L b is the reflected path length of the acoustic signal at one time.
  • L b can be given by:
  • L b AL + L 'a '
  • L a is the reflected path length of the acoustic signal at another time
  • AL is the change of the two reflected path lengths, given by:
  • the spatial surface fluctuation Ah is linearly related to the phase fluctuations by: ⁇
  • processing module 130 uses this result to scale phase fluctuations into spatial surface fluctuations. Therefore, it can be seen that a time-series for surface fluctuations can be obtained.
  • the steps 350-370 can be performed in the same repeating loop as steps 310-340, or they may be deferred to an offline processing step, based on a recording of the phase shifts made in step 340. This is a matter of design choice, depending whether the apparatus is required to report height fluctuations in real time, or the measurements are required only for offline analysis.
  • the height measurement step 350 can be repeated at intervals, which may for example be longer intervals than the intervals between the packets for the steps 310-340.
  • the height measurement data if it varies over time, can be recorded in association with the phase shift data for the packets, to allow steps 360 and 370 to be performed at a later time.
  • FIG. 7 shows two sets of graphs with each graph illustrating the water surface fluctuation Ah in 10" 3 m over time t in seconds as measured by a conventional conductance probe (solid trace) and by an acoustic probe forming an embodiment of the present invention (dashed trace).
  • the conventional conductance probe in the experiment was a Churchill Controls 0.25 mm, 2-core conductance probe. From each of the graphs shown in Figure 7, it can be seen that, although there are two traces, they follow one another closely.
  • the water surface fluctuation Ah as measured from a phase variation substantially corresponds to the water surface fluctuation Ah as measured from conventional conductance probes known in the art.
  • Analysis of an individual time series allows for calculation of spectral and/or statistical parameters of the surface fluctuations.
  • the root mean square wave height of the liquid surface can be calculated. This is a very useful characteristic that can be used to determine various hydraulic quantities such as flow depth, mean flow velocity, turbulence intensity, hydraulic roughness and boundary shear stress. A spatial spectrum from each microphone may also be calculated which is believed will yield further details of the hydraulic conditions.
  • Figure 8(a) shows experimental results comparing the root mean square wave height of the liquid surface (horizontal axis), measured using the new acoustic method, and mean flow velocity v (vertical axis) in an experimental flowing stream.
  • the strong correlation between the two variables implies that the RMS wave height can be used to estimate the mean flow velocity in a real water course.
  • Figure 8(b) is a plot of the measured RMS wave height against the hydraulic resistance coefficient (k s ) which is a standard measure of the hydraulic roughness of an open channel.
  • the hydraulic roughness of an open channel is related to the roughness of the channel bed, as described for example in 'Experiments with Fluid Friction in Roughened Pipes' by Colebrook and White in Proceedings of the Royal Society of London, Series A, Mathematical and Physical Sciences 161(906): 367-381. Again, a strong correlation can be observed which implies that the acoustic wave height measurement can be used to estimate hydraulic roughness in a real water course.
  • Figure 9 is a graph showing correlation coefficients CORR observed between the acoustic signals measured by a pair of receivers (microphones) separated by a different distance SEP.
  • the plotted points trace a correlation function which depends on the characteristics of the surface fluctuations in the observed conditions.
  • a 'correlation radius' defined for example as the separation SEP at which correlation drops to 0.1, is around 2-3 cm.
  • the apparatus described above to calculate the correlation function, by measuring correlation at a number of different separations, another tool is provided for analysis of water surface correlation radius, which can be used to determine various hydraulic quantities such as flow depth, mean flow velocity, turbulence intensity, hydraulic roughness and boundary shear stress.
  • the correlation function can be calculated in addition to direct recording of the surface fluctuations from one or more of the receivers involved.
  • the correlation radius in a given situation also gives an idea of the radius of the insonified zone that will give the best combination of responsiveness and freedom from spurious signals, when designing or adjusting the apparatus.
  • measurement of correlation at different separations can be facilitated by providing an array of receivers with different spacings, all receiving simultaneously. A certain number of microphones, if appropriately spaced, can be selected and paired to give a much greater number of unique separations between them, so as to obtain sufficient samples separations to estimate the correlation function for the intensity of the acoustic field scattered by a water surface.
  • the correlation at different separations can be measured sequentially, using a pair of receivers with variable separation.
  • an additional receiver array can be provided orthogonal to the first (so they form a cross), or even a grid of receivers. This allows for measurements to be spatially distributed in two dimensions across the surface, allowing 3-D surface properties to be quantified rather than just 2-D.
  • the spatial correlation function allows us to determine the characteristic spatial period, which we find to scale very similarly to the wave height in response to a change in hydraulic conditions, and therefore also correlates with the flow depth, velocity, discharge etc.
  • Figures 10 to 12 show additional experimental results illustrating the above utility.
  • Figure 10 shows a relationship between measured surface roughness (RMS wave height) ⁇ and the (volumetric) flow rate of water in a channel.
  • Figure 11 shows relationships between surface roughness ⁇ and the depth of flowing water DEP.
  • the experiment was repeated for a number of different bed slopes (pipe gradients) SI, S2, S3, S4, showing that the surface characteristics can be used to distinguish different bed slopes also.
  • Figure 12 shows a relationship between roughness spatial period P bed shear stress ⁇ . The bed shear stress is related to sediment transport. In all the graphs illustrated, the measured points fit the linear relationships very closely.
  • the acoustic instrument described above can be termed a 'spatiotemporal acoustic wave-monitor' since it measures the spatial and temporal properties of the surface waves.
  • this measurement could only be achieved by conductance probes which are very invasive, or by particle image velocimetry which is very expensive.
  • the novel spatiotemporal wave monitor can then be used to understand the meaning behind the observed spatiotemporal flow surface properties, and thereby infer highly valuable information about the flow, which previously could not be remotely measured.
  • a component can be, but is not limited to being, a process running on a processor, an object, a code module, a thread of execution, a program, and/or a computer.
  • an application running a computing device and the computing device can be a component.
  • One or more components can reside within a process and/or thread of execution and a component can be localised on one computer and/or distributed between two or more computers.
  • these components can be executed from various computer readable media having various data structures stored therein.
  • the components can communicate by way of local and/or remote process such as in accordance with a signal having one or more data packets (e.g. data from one component interacting with another component in a local system, distributed system, and/or across a network such as the Internet with other systems by way of signal).
  • a signal having one or more data packets (e.g. data from one component interacting with another component in a local system, distributed system, and/or across a network such as the Internet with other systems by way of signal).
  • the embodiments described herein can be implemented in hardware, software, firmware, middleware, microcode, or any combination thereof.
  • the invention may take the form of a computer program containing one or more sequences of machine-readable instructions which, when executed by a computer, control the components of a system described above to perform a method described above.
  • the processing units can be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.
  • ASICs application specific integrated circuits
  • DSPs digital signal processors
  • DSPDs digital signal processing devices
  • PLDs programmable logic devices
  • FPGAs field programmable gate arrays
  • processors controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.
  • a code segment can represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements.
  • a code segment can be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. can be passed, forwarded, or transmitted using any suitable means including memory sharing, message passing, token passing, network transmission, etc.
  • the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein.
  • the software codes can be stored in memory units and executed by processors.
  • the memory unit can be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Fluid Mechanics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electromagnetism (AREA)
  • Thermal Sciences (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

Dynamic characteristics of a liquid surface (160) are measured by sending acoustic signals (140) to or more target areas (162a-162c) on the liquid surface and receiving said acoustic signals (150a-150c) after reflection from the target area. The detected signals are processed to measure phase shift between the sent and received acoustic signals, the measured phase shift varying over time. The varying phase shift is used to indicate fluctuations over time in the local height of the liquid surface in the target area. The liquid may be water, effluent etc. flowing in a channel or conduit. With suitable calibration, the measured height fluctuations can be used to infer flow characteristics such as surface roughness, wave height, flow depth, flow velocity, volumetric flow rate, shear stress, sediment transport. Using an array of receivers and target areas, additional spatial and temporal characteristics of the surface and the flow can be measured.

Description

METHODS AND APPARATUS FOR DETECTION OF FLUID INTERFACE FLUCTUATIONS FIELD
The present invention relates generally to acoustic technologies, and more particularly to methods and apparatus for detection of fluctuations in an interface between two fluids. The invention further relates to processors and computer program products adapted for use in such methods.
BACKGROUND
An example of an interface between two fluids is the free surface of a liquid (first fluid) under a gaseous atmosphere (second fluid). The liquid may be relatively static, with surface fluctuations caused by wind, for example. The liquid may be flowing in a conduit or channel with surface fluctuations (waves) caused additionally by turbulence. It is important to monitor flow conditions of free-surface flow in a number of applications, such as river flood monitoring, flow control in water and waste treatment, petrochemical and food processing plants.
It has been disclosed by Nichols, A. et al, in Sonic Characterisation of Water Surface Waves, ISPF2010, Nanjing, China in 2010, and by Liu, H.-T., K. B. Katsaros and M. A. Weissman in Dynamic Response of Thin-Wire Wave Gauges, J. Geophys. Res., 87(C8), 5686-5698 in 1982 that detailed surface fluctuations can be captured by use of invasive conductance probes. However, these probes may collect debris in the flow and generate their own surface fluctuations which can obscure data.
It is known to use ultrasonic devices to gauge the relative position of a water surface in order to calculate depth. These operate with airborne acoustic signals to measure the surface height in a static or average way, for example to measure the fill state of a storage tank, or the state of a tide. Airborne Doppler techniques are known to be used to quantify the horizontal component of surface velocity of water flows. Other airborne time-of-flight acoustic range finding techniques have been used to measure the static level of water by emitting short pulses (e.g. N. A. Bolton, Liquid Level Indication System, US Patent 3,184,969, June 10, 1963; S. D. Lenz, R. Hulinsky, Ultrasonic Level Measuring System, US Patent 5,319,974, June 14, 1994, and also GB 1600079, GB 2188420A, GB 2472085A, US 2006/0037392A1). Some underwater acoustic techniques have been known to measure the statistical roughness of a water surface, for example to monitor sea state at offshore locations. An example is the work by E. I. Thorsos, "The validity of the Kirchhoff approximation for rough surface scattering using a Gaussian roughness spectrum", J. Acoust. Soc. Am., 83(1), 78-92 (1988). An ultrasonic device for measuring surface roughness of mechanical components is disclosed in US 4364264. None of the known acoustic devices offers the ability to measure detailed local surface fluctuations at a fluid interface, in a way that could allow them to replace the invasive conductance probes in the investigation and monitoring of flow conditions.
SUMMARY
Various embodiments of the present invention provide non-invasive methods and systems for detection of fluctuations in fluid interfaces such as free surfaces of flowing liquid, thereby to address one or more of the drawbacks of the aforementioned prior art.
According to a first aspect of the invention, there is provided a method for measuring dynamic characteristics of an interface between two fluids, the method comprising:
sending acoustic signals from an acoustic source to at least one target area on the fluid interface;
receiving said acoustic signals at an acoustic receiver after reflection from the target area; and,
processing the detected signals to measure phase shift between the sent and received acoustic signals, the measured phase shift varying over time, and using the variations in phase shift to indicate fluctuations over time in the position of the fluid interface in the target area.
To allow accurate indication of dynamic, local fluctuations, the target area can be designed to have a size smaller than a dominant spatial scale of said localised fluctuations at the interface.
In a particular application of the method, said two fluids are a gas (which includes a vapour) and a liquid, said interface being a free surface of the liquid, the acoustic source and receiver being positioned above the liquid surface, the variations in phase shift being used indicate fluctuations over time in the height of the liquid surface.
The liquid may be flowing in a natural or man-made channel or conduit. In embodiments of the invention the method further comprises deriving from the measured variations in phase shift a characteristic of the flowing liquid such as: surface roughness, wave height, flow velocity, volumetric flow rate, shear stress, sediment transport. The sent acoustic signals may comprise a harmonic sine wave. Said processing step may comprise comparing phases of the sent and received signals over several cycles of said sine wave to obtain a measurement of said phase shift at a given time.
The phase shift may be is determined on the basis of Hilbert transforms of data representing the sent and detected acoustic signals.
The method may further comprise arranging a plurality of acoustic receivers at different positions relative to the acoustic source so as to receive acoustic signals that have reflected simultaneously from different target areas on the fluid interface and processing the received acoustic signals so as to measure a time-varying phase shift corresponding to each of said target areas. The plurality of receivers may be spaced to allow different separation distances between different pairs of the receivers. The plurality of receivers may be spaced in two dimensions so that said different target areas are spaced in two dimensions over the fluid interface.
The method may further comprise measuring a temporal lag between fluctuations measured for different target areas (i.e. by different receivers). A flow velocity may be derived from the temporal lag and from knowing the distance between the target areas in a direction fo fluid flow.
The method may further comprise determining a wave height at the target area on the basis of the measured variations in phase shift, a known separation of the acoustic source and receiver and a known receiver height relative to said interface. Said known receiver height may be obtained by measuring a time of flight of an acoustic signal sent from said acoustic source, and received by said acoustic receiver following reflection from the interface.
The invention further provides apparatus as defined in the appended claims, which may be used to perform the methods of the invention, as set forth above. In another aspect of the invention, a method for detecting liquid surface fluctuations comprises: sending acoustic signals from a first known point to a point on a liquid surface; receiving said acoustic signals at a second known point after reflection from the liquid surface; processing the detected signals periodically to monitor variations in phase shift between the sent and received acoustic signals, and using the variations in phase shift to indicate fluctuations in the height of the liquid surface at the point. According to another aspect of the invention, a system for detecting liquid surface fluctuations comprises: a signal emission module operable to send acoustic signals from a first known point to a point on a liquid surface; a signal detection module operable to receive said acoustic signals at a second known point after reflection from the liquid surface; and a processing module operable to process the detected signals periodically to monitor variations in phase shift between the sent and received airborne acoustic signals, and using the variations in phase shift to indicate fluctuations in the height of the liquid surface at the point.
According to yet another embodiment of the invention, there is provided a processor operable to process sent and received acoustic signals of the above method for detecting fluid interface liquid surface fluctuations.
According to yet another embodiment of the invention, there is provided a computer-readable medium including instructions which when executed by a computer can process sent and received acoustic signals of the above method for detecting liquid surface fluctuations.
The above and other aspects, features and advantages of the invention will be understood by the skilled reader from a consideration of the following detailed description of exemplary embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. Figure 1 is a schematic side view of an exemplary system for detecting liquid surface fluctuation according to one embodiment of the present invention.
Figure 2 shows an example of a signal detection module having a plurality of receivers to receive acoustic signals in (a) schematic side view and (b) and (c) plan views of different variants. Figure 3 is a flowchart of an exemplary method for detecting liquid surface fluctuation according to one embodiment of the present invention.
Figure 4 is a flowchart of an exemplary method for detecting liquid surface fluctuation according to another embodiment of the present invention.
Figure 5 is a flowchart of an exemplary method for determining the height of signal detection module above the liquid surface, usable in the methods of Figures 3 and 4.
Figure 6 is an explanatory illustration of path lengths of two acoustic signals travelling from the signal emission module 110 to the signal detection module 120.
Figure 7 is a set of graphs showing the water surface fluctuation Y over time X as measured by a conventional conductance probe and by an acoustic probe forming an embodiment of the present invention.
Figure 8 is a set of graphs demonstrating the relationship of the measured water surface RMS surface roughness σ to (a) mean flow velocity v and (b) hydraulic roughness ks.
Figure 9 is a graph showing correlation coefficients varying with receiver separation.
Figure 10 demonstrates a relationship between volumetric flow rate F and measured water surface roughness.
Figure 11 demonstrates relationships between depth of flowing water and measured water surface roughness, for various bed gradients. Figure 12 demonstrates a relationship between flow surface characteristic period P and shear stress τ at a channel bed.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiments may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.
While the invention may be applied generally to any interface between two fluids, the examples will use the practical example of a free surface of a liquid, that is to say the interface between a body of liquid such as water and a body of gas above it, for example the open atmosphere or atmosphere above the liquid within a closed conduit.
Figure 1 shows an exemplary system 100 for detecting liquid surface fluctuation in accordance with various embodiments presented therein. System 100 comprises a signal emission module (emitter for short) 110, a signal detection module (receiver for short) 120 and a processing module 130. System 100 can be deployed to detect fluctuations in the height at a point 162 on a liquid surface 160. The fluctuation over time may be represented by as a wave height at the point 162. In practice, point 162 will not be an infinitely small point, but rather a target area. By suitable design of the system, the size of the target area can be made small relative to the surface fluctuations that are to be monitored, as discussed further below. System 100 may be positioned above the liquid surface 160 or below the liquid surface 160. In one embodiment, system 100 is operable to perform airborne acoustic inspection of hydraulic flow in shallow water channels, rivers, partly filled pipes and other unpressurised conduits. A flow with velocity v is indicated schematically by an arrow. The modules 110 and 120 may be mounted beneath a bridge over a river, in the roof of a conduit, or on their own platform, according to convenience. In practice, the fluctuations caused by turbulence and other mechanisms in such a real-world system will be more complex and three-dimensional than the simple wave shape shown in Figure 1. Also, the height of the fluctuations is greatly exaggerated in Figure 1, relative to the scale of the apparatus as a whole.
Signal emission module 110 comprises a signal generator and a transducer operable as an acoustic source to emit one or more airborne acoustic signals. Receiver 120 comprises a microphone or other transducer operable as an acoustic receiver to detect the one or more acoustic signals after reflection from a small target area the liquid surface. Processing module 130 is capable of data communication with emitter 110 or receiver 120 via a cable or wirelessly. For example, wireless data communication may be a short range wireless communication via a short distance data transmission technology standard such as Bluetooth (RTM). Processing module 130 may be a mobile personal computer, a handheld device or other computing device.
In an embodiment, emitter 110 is mounted at an angle between ten and eighty degrees to the horizontal, which may, for example, be approximately forty-five degrees. The emitter 110 may include an array of acoustic transducers, each of which is operable to emit an acoustic signal. In that case, controlling the relative phases of the emitted signals allows the direction and directivity of the acoustic signal to be controlled. Actively steering the beam is an option, for example to adjust for different surface heights, though it would add to cost and may reduce robustness of a device. Alternatively, one can design the geometry of the emitter-receiver arrangement such that the receiver is within the reflected beam for all reasonable flow depths, and use active steering when this is not possible.
In operation, processing module 130 controls emitter 110 to emit acoustic signals 140 over an extended period of time Processing module 130 triggers receiver 120 to receive airborne acoustic signals 150 reflecting back from surface 160 and processes the received signals on a continuous or pseudo-continuous basis. The signals follow different paths as the surface moves over time. The surface at different times may have different shapes illustrated by the solid and broken curves 160 and 160'. Correspondingly, the path of the acoustic signals may be as shown in the solid lines 140 & 150 at one time, and as shown by the broken lines 140' & 150' at another time.
The signal emission module (emitter) 110 in a simple embodiment emits a continuous ultrasonic sine wave at the resonant frequency of emitter 110 such as 45 kHz, and at an angle of, for example, 45 degrees to the horizontal. For example, the emitted acoustic signal may be configured to be a monochromatic sine wave at the resonant frequency of the transducer. The wavelength [ λ ) of the acoustic signal may be selected to be comparable with the maximum amplitude of the water surface roughness or greater than the root mean square of the water surface roughness height ( A≥ σ ), and a continuous harmonic signal may be emitted.
Figure 2 (a) shows an embodiment of system 100 in which signal detection module 120 comprises a horizontal array of receivers 122a, 122b, 122c etc., such as microphones, spaced horizontally from emitter 110 with different distances Dl, D2, D3. As an example, the array of microphones may be installed and mounted on the same horizontal axis as emitter 110 and at a distance in front of emitter 110 equal to twice the approximate height above liquid surface 160, where the incidence angle is 45 degrees. Alternatively, the microphones can be arranged in the form of a vertical array to cover the same range of angles of incidence. Each microphone 122a etc. will receive acoustic signals 150a etc. which have been reflected from a different area 162a, etc. within the insonified elliptical zone of the surface. The size of this insonified zone is determined by the distance to the liquid surface from the emitter transducer, the directivity of the acoustic signal (that is the ratio of the acoustic wavelength to the transducer dimension λ I d ) and the incidence angle. For a stable operation, the dimensions of this zone should be chosen to be comparable to the correlation radius of the dynamic water surface roughness. The distance between the transducer and the water surface is chosen to satisfy the far-field conditions, i.e. La » 2d 2 1 λ where La is the reflected path length.
A target area on the surface from which a dominant acoustic signal is received at a particular receiver is designed to be small in relation to a dominant spatial scale of said localised fluctuations at the liquid surface. Various considerations can be taken into account to design a practical system in which the area measured is small. First, the beam of sound projected can be is relatively directional, as already described. The amplitude of the emitted sound pressure thus strongly depends on the angle of incidence which is maximum in the direction of specular reflection to the receiver(s). Secondly, the area of the flow surface which carries key phase information about the water surface elevation is small by designing the system to exploit the Fresnel zone effect. According to this effect, sound reflections produced by the parts of the illuminated surface, which are much farther than the wavelength from the point of specular reflection, do not influence strongly the phase of the recorded signal and simply cancel out at the reception point. For this purpose the acoustic wavelength is carefully selected to minimise the Fresnel zone dimensions. The acoustic wavelength may be less than 15 cm, less than 10 cm for example. Thirdly, the characteristic spatial period of the flow surface roughness is assumed to be large in comparison with the acoustic wavelength, so that any reflections from outside the Fresnel zone are deemed to be uncorrelated with the signal received through the angle of specular reflection. The frequency of sound can be carefully selected to ensure that, and phase comparisons can incorporate a sufficient number of cycles to eliminate uncorrelated signal components. Implementing a plurality of receivers allows for analysis of acoustic data reflected from different areas of the surface and allows for water surface roughness with different correlation radii to be analysed. Additionally, a plurality of receivers arranged along a horizontal axis allows for mean surface gradient deduction by measurement of reflected path-length from emitter 110 to each respective receiver of receiver 120. The distances Dl, D2, D3 etc. are chosen such that each possible paring of receivers give rise to a unique separation between them. For example, four microphones may have six possible parings. Each receiver has an associated channel to output its received signal to processing module 130.
As shown in the plan views of Figure 2 (b) and (c), different arrangements of the plural receivers and the source can be devised, according to the types of measurement desired, the costs and so forth. In (b) the receivers 122a to 122c are shown spaced away from emitter 110 along a line parallel with the general flow direction of the liquid being monitored. They could be arranged transversely or obliquely to the flow direction if desired. In Figure 2 (c) a larger number of receivers are arranged in a two-dimensional grid pattern, so as to measure at various points across the stream. A simply 'crosshairs' arrangement can be provided, as shown in solid lines, or a more elaborate array of receivers can be provided as indicated by the dotted receivers. The emitter in these examples is shown to one side of the receiver array, but can be placed within it, for example at the centre of a crosshair or grid arrangement. Such an arrangement may be more compact. The emitter in that case may point vertically, or may comprise a number of emitters inclined outward from vertical. For each receiver, the received acoustic signals of course are reflected from a target point or area mid-way between the receiver and the source, as seen in the side view of Figure 2(a). Therefore the overall surface area sampled by the small target areas is half the size (in each dimension) of the array of receivers.
In one embodiment, processing module 130 is triggered to acquire acoustic data in packets at a frequency high enough to capture surface fluctuation but low enough to conserve memory and processing power. The triggering frequency depends on the nature of the surface fluctuations, which may for example be between lHz and 500Hz. In one embodiment, the triggering frequency is 100Hz and the number of acquired sinusoidal periods of data for each trigger is greater than 10. In a simple embodiment, as mentioned above, the emitter 110 emits a continuous sine wave, whose phase and frequency are stable over the time period between sending and receiving acoustic signals from the liquid surface. In an alternative embodiment, the emitter 110 is triggered to emit signals only in packets, synchronised with the received packets. This may be desired for example to conserve energy, and also to permit other uses of the transducer between packets. Whether the emission of the acoustic signals is continuous or broken into packets, the emitting and receiving modules must be synchronised so that the phase of the sent and received signals can be compared with suitable accuracy. As one option, the sine wave may be continuously generated, so as to be available for comparison with the received signal, while its amplification and output to the emitting transducer is gated so that the acoustic signal is only emitted in packets.
The processing module 130 may be operable to acquire a packet (as an example, each packet may be 1ms) of acoustic data at each trigger from receiver 120 and determine a phase shift of each acoustic signal between the emitted signal and the received signal. Processing module 130 is operable to sample the acoustic data at a frequency greater than the Nyquist frequency of twice the frequency of the emitted signal. The sampling frequency may be at least ten times the emitted acoustic signal frequency and in one embodiment may be lMHz. Processing module 130 may also be operable to band-pass filter each packet of acoustic data to isolate the transmission frequency of emitter 110, and to analyse each packet of acoustic data to extract the phase shift between the emitted and received signals. There are a number of means to determine the phase shift between the emitted and received signals, for example: the 'product- to-sum' trigonometric identities; a phase measurement of the cross-correlation between the two harmonic signals; or Hilbert transforms of the sent and detected acoustic signals; or the dot product method. It is understood that the processing module 130 is not limited by using a particular means of determining the phase shift between the emitted and received signals. Instead, processing module 130 is interpreted to cover any means which may be employed to determine a phase shift between the emitted and received signals.
For each packet, processing module 130 is operable to average the phase shift measured and unwrapped at different points within the packet, to give a phase shift value for that packet. The instantaneous phase of the received signal at each microphone is thereby known for each packet. Since the packet triggering frequency is known, a time can be associated with each phase measurement. The processing module may be operable to provide a time series of phase shifts, from which phase variations representing surface fluctuations can be observed. Figure 3 is a flowchart illustrating the general principle of detecting liquid surface fluctuation with reference to the components disclosed in system 100. At step 210, emitter 110 can send acoustic signals 140 and 150 towards the point 162 of the liquid surface 160 at a first time and a second time, respectively. At step 220, receiver 120 receives acoustic signals 140 and 150 reflecting back from the point 162 at a third time and a fourth time, respectively.
At step 230, processor module 130 determines a first phase shift of the first acoustic signal and a second phase shift of the second acoustic signal. The first phase shift indicates a time- dependent phase shift of the first acoustic signal between the first time and the third time. The second phase shift indicates a time-dependent phase shift of the second acoustic signal between the second time and fourth time.
At step 240, processor module 130 determines phase variation information on the basis of the first phase shift and the second phase shift. If the liquid surface 160 is stationary (or at least is at the same place when the two acoustic signals are reflected), the value of the first phase shift is same to the value of the second phase shift. Consequently, the value of the phase variation is zero and indicates that there is no fluctuation at point 162.
If the liquid surface 160 displaced vertically, the value of the first phase shift is different with the value of the second phase shift. Consequently, the value of the phase variation is altered due to a change in acoustic signal transmission length. As a result, the phase variation is capable of indicating the surface fluctuations on an arbitrary scale and thus allowing emitter 110 and receiver 120 to be positioned anywhere above the air-water interface.
Figure 4 is a flowchart of a method 300 comprising an embodiment of the invention based on the method 200 described above. In exemplary method 300, steps 310-340, and optionally further steps, are repeated in a continuous loop, while surface fluctuations are to be measured. At step 310, emitter 110 emits acoustic signals in sine wave form. The signals may be emitted as a continuous sine wave or in discrete packets. At 320, receiver 120 is triggered synchronously with the emitter and it receives a packet of acoustic data.
At step 330, processing module 130 calculates Hilbert Transforms of the sent and received acoustic data. The Hilbert Transforms of the sent acoustic signal Vs(t) and the received acoustic signal Vr(t) are defined by the following: Vs (t) = As (t)e i(os t + i(p
Vr{i)
Figure imgf000014_0001
, respectively.
Here As and Ar are the amplitudes of the sent and received acoustic data respectively, cos is the emitter 110 excitation frequency, and cps is the phase of the sent acoustic data at time t = 0. At step 340, processing module 130 determines the phase shift for each packet of acoustic data from the Hilbert Transforms. This is done by taking the natural logarithm of the ratio of the analytic signals, the imaginary part IM of this being the time dependent phase shift, Δφ (ί) , between the sent and received acoustic data:
Figure imgf000014_0002
For each packet of acoustic data, the calculated phase shifts are averaged to give a single phase shift for that packet.
Since the packet triggering frequency is known, a time can be associated with each phase measurement. Processing module 130 can thus form a time series of phase fluctuations between + π and—π . At step 350, processing module 130 tracks the phase gradient and its sign of each phase fluctuation so that phase differences that exceed + π and - π can be extracted. These phase differences are associated with surface height fluctuations exceeding acoustic wavelength A . In one embodiment, the acoustic wavelength of the acoustic signal from the emitter 110 is 7.6 mm. Tracking phase differences greater than + π and—π is therefore important for tracking surface height fluctuations greater than a few millimetres. Processing routines, for example 'unwrapping' functions in Matlab, for example, are readily available to implement this function to follow the phase variations over a range greater than ± π .
At optional step 360, processing module 130 can obtain the height of receiver 120 above the liquid surface so that the arbitrarily scaled phase fluctuations so far calculated can be scaled as required. Where the height of the receiver 120 above the surface is unknown, the height may be obtained by processing module 130 in accordance with an exemplary method as described below. Figure 5 illustrates such a method. At step 410, emitter 110 sends an acoustic short pulse signal to the liquid surface 160. At step 420, receiver 120 receives the acoustic signal. At step 430, processing module 130 obtains the time for the acoustic signal travelling from emitter 110 to receiver 120. At step 440, processing module 130 calculates the reflected path length of the acoustic signal travelling from emitter 110 to receiver 120, using the known value for the speed of sound in air. At step 450, since the distance between the emitter 110 and the receiver 120 is known, the processing module 130 can use the distance and the reflected path length calculated at step 440 to calculate the height of receiver 120 above the liquid surface, using the Pythagoras theorem.
Returning to Figure 4, at step 370, the measured height is used to calculate a scale factor for use in converting measured phase variations (measured by angle) into liquid surface height variations (measured in millimetres). Details of this calculation will be given below.
Referring to the method of Figure 5 and also the geometry illustrated in Figure 6, the spatial surface fluctuation Ah is calculated according to:
Figure imgf000015_0001
where h is the height of receiver 120 above surface 160, D is the distance between emitter 110 and receiver 120, and Lb is the reflected path length of the acoustic signal at one time. Lb can be given by:
Lb = AL + L 'a ' where La is the reflected path length of the acoustic signal at another time, and AL is the change of the two reflected path lengths, given by:
Αφλ
AL , where λ is the acoustic wavelength, and
Figure imgf000015_0002
Therefore, the spatial surface fluctuation Ah is linearly related to the phase fluctuations by: Αφλ
Ah cos(0 - A0) ,
2π where Θ is the incidence angle of the emitter 110 and ΑΘ is the deviation from the incidence angle. Since Αθ «θ , the relationship is thus:
Αφλ
Ah cos(0)
2π This last equation shows the scaling required for converting a phase variation to a height variation. At step 370, processing module 130 uses this result to scale phase fluctuations into spatial surface fluctuations. Therefore, it can be seen that a time-series for surface fluctuations can be obtained.
The steps 350-370 can be performed in the same repeating loop as steps 310-340, or they may be deferred to an offline processing step, based on a recording of the phase shifts made in step 340. This is a matter of design choice, depending whether the apparatus is required to report height fluctuations in real time, or the measurements are required only for offline analysis. The height measurement step 350 can be repeated at intervals, which may for example be longer intervals than the intervals between the packets for the steps 310-340. The height measurement data, if it varies over time, can be recorded in association with the phase shift data for the packets, to allow steps 360 and 370 to be performed at a later time. In principle, one could also store the received acoustic data and perform the phase comparison (by Hilbert transform or by other means) offline. To calculate and store the phase shifts (or phase variations) in real time will normally require far less storage and data handling. Figure 7 shows two sets of graphs with each graph illustrating the water surface fluctuation Ah in 10"3 m over time t in seconds as measured by a conventional conductance probe (solid trace) and by an acoustic probe forming an embodiment of the present invention (dashed trace). The conventional conductance probe in the experiment was a Churchill Controls 0.25 mm, 2-core conductance probe. From each of the graphs shown in Figure 7, it can be seen that, although there are two traces, they follow one another closely. This confirms that, at least under the test conditions, the water surface fluctuation Ah as measured from a phase variation substantially corresponds to the water surface fluctuation Ah as measured from conventional conductance probes known in the art. Analysis of an individual time series allows for calculation of spectral and/or statistical parameters of the surface fluctuations. As an example, the root mean square wave height of the liquid surface can be calculated. This is a very useful characteristic that can be used to determine various hydraulic quantities such as flow depth, mean flow velocity, turbulence intensity, hydraulic roughness and boundary shear stress. A spatial spectrum from each microphone may also be calculated which is believed will yield further details of the hydraulic conditions.
Figure 8(a) shows experimental results comparing the root mean square wave height of the liquid surface (horizontal axis), measured using the new acoustic method, and mean flow velocity v (vertical axis) in an experimental flowing stream. The strong correlation between the two variables implies that the RMS wave height can be used to estimate the mean flow velocity in a real water course.
Similarly, Figure 8(b) is a plot of the measured RMS wave height against the hydraulic resistance coefficient (ks) which is a standard measure of the hydraulic roughness of an open channel. The hydraulic roughness of an open channel is related to the roughness of the channel bed, as described for example in 'Experiments with Fluid Friction in Roughened Pipes' by Colebrook and White in Proceedings of the Royal Society of London, Series A, Mathematical and Physical Sciences 161(906): 367-381. Again, a strong correlation can be observed which implies that the acoustic wave height measurement can be used to estimate hydraulic roughness in a real water course.
Figure 9 is a graph showing correlation coefficients CORR observed between the acoustic signals measured by a pair of receivers (microphones) separated by a different distance SEP. The correlation function when SEP=0 is 1 by definition. As the separation increases, the plotted points trace a correlation function which depends on the characteristics of the surface fluctuations in the observed conditions. In the conditions illustrated, a 'correlation radius', defined for example as the separation SEP at which correlation drops to 0.1, is around 2-3 cm. As the separation increases, there is a negative peak (anti-correlation) around 7 cm, a zero around 12 cm, a positive peak around 16 cm and so on. Using the apparatus described above to calculate the correlation function, by measuring correlation at a number of different separations, another tool is provided for analysis of water surface correlation radius, which can be used to determine various hydraulic quantities such as flow depth, mean flow velocity, turbulence intensity, hydraulic roughness and boundary shear stress. The correlation function can be calculated in addition to direct recording of the surface fluctuations from one or more of the receivers involved.
The correlation radius in a given situation also gives an idea of the radius of the insonified zone that will give the best combination of responsiveness and freedom from spurious signals, when designing or adjusting the apparatus. Referring again to Figure 2, it will be recalled that measurement of correlation at different separations can be facilitated by providing an array of receivers with different spacings, all receiving simultaneously. A certain number of microphones, if appropriately spaced, can be selected and paired to give a much greater number of unique separations between them, so as to obtain sufficient samples separations to estimate the correlation function for the intensity of the acoustic field scattered by a water surface. In an alternative embodiment, the correlation at different separations can be measured sequentially, using a pair of receivers with variable separation. The separations in the example described are assumed to be in a horizontal in this example, but that is not necessarily so. As already illustrated in Figure 2 (c), an additional receiver array can be provided orthogonal to the first (so they form a cross), or even a grid of receivers. This allows for measurements to be spatially distributed in two dimensions across the surface, allowing 3-D surface properties to be quantified rather than just 2-D.
Further to the above discussion of a spatial correlation function by analysis of the temporal correlation peaks between pairs of receivers, one can also measure the temporal lag (time delay) at which this peak occurs. Where it is the case that that the surface roughness is predominantly due to turbulence and not extraneous factors such as wind or vibration, this temporal lag can be used to obtain a second measurement of flow velocity (additional to the empirical relationships presented previously). Since the separation of the two specular reflection points is known (half the separation of the receivers), a flow velocity can be calculated from the spatial separation and the temporal lag between the phase shift variations at two microphones (receivers). This can be performed for multiple microphone pairs in order to reduce error. Similarly Doppler techniques can be used, as already mentioned.
We could also mention that the spatial correlation function allows us to determine the characteristic spatial period, which we find to scale very similarly to the wave height in response to a change in hydraulic conditions, and therefore also correlates with the flow depth, velocity, discharge etc. Experiments confirm the relationships described above and confirm utility of the described system for investigating and/or monitoring hydraulic flow conditions in real applications, thanks to the relationships between flow conditions and surface structure. A change in bed structure should also cause a noticeable effect in the surface shape. We have also seen that the surface pattern seems to respond to changes in the bed transport, giving the potential for the sediment transport rate to be measured remotely.
Figures 10 to 12 show additional experimental results illustrating the above utility. Figure 10 shows a relationship between measured surface roughness (RMS wave height) σ and the (volumetric) flow rate of water in a channel. Figure 11 shows relationships between surface roughness σ and the depth of flowing water DEP. The experiment was repeated for a number of different bed slopes (pipe gradients) SI, S2, S3, S4, showing that the surface characteristics can be used to distinguish different bed slopes also. Figure 12 shows a relationship between roughness spatial period P bed shear stress τ. The bed shear stress is related to sediment transport. In all the graphs illustrated, the measured points fit the linear relationships very closely.
In conclusion, the acoustic instrument described above can be termed a 'spatiotemporal acoustic wave-monitor' since it measures the spatial and temporal properties of the surface waves. Previously, (to our knowledge) this measurement could only be achieved by conductance probes which are very invasive, or by particle image velocimetry which is very expensive. The novel spatiotemporal wave monitor can then be used to understand the meaning behind the observed spatiotemporal flow surface properties, and thereby infer highly valuable information about the flow, which previously could not be remotely measured.
As used in this application, the terms "component", "module", "system" and the like are intended to refer to a computer-related entity, either hardware, firmware, a combination of hardware and software, or software in execution. For example, a component can be, but is not limited to being, a process running on a processor, an object, a code module, a thread of execution, a program, and/or a computer. By way of illustration, both an application running a computing device and the computing device can be a component. One or more components can reside within a process and/or thread of execution and a component can be localised on one computer and/or distributed between two or more computers. In addition, these components can be executed from various computer readable media having various data structures stored therein. The components can communicate by way of local and/or remote process such as in accordance with a signal having one or more data packets (e.g. data from one component interacting with another component in a local system, distributed system, and/or across a network such as the Internet with other systems by way of signal).
While specific embodiments of the invention have been described above, it is to be understood that the embodiments described herein can be implemented in hardware, software, firmware, middleware, microcode, or any combination thereof. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions which, when executed by a computer, control the components of a system described above to perform a method described above.
For a hardware implementation, the processing units can be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.
When the embodiments are implemented in software, firmware, middleware or microcode, program code or code segments, they can be stored in a machine-readable medium, such as a storage component. A code segment can represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment can be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. can be passed, forwarded, or transmitted using any suitable means including memory sharing, message passing, token passing, network transmission, etc.
For a software implementation, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes can be stored in memory units and executed by processors. The memory unit can be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.
The term "comprising", "including" and the like as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality. The methods described above are not limited by the order of acts, as some acts can, in accordance with one or more embodiments, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts can be required to implement a methodology in accordance with one or more embodiments.
The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that various modifications may be made to the invention as described without departing from the spirit and scope of the invention.

Claims

1. A method for measuring dynamic characteristics of an interface between two fluids, the method comprising:
sending acoustic signals from an acoustic source to at least one target area on the fluid interface;
receiving said acoustic signals at an acoustic receiver after reflection from the target area; and,
processing the detected signals to measure phase shift between the sent and received acoustic signals, the measured phase shift varying over time, and using the variations in phase shift to indicate fluctuations over time in the position of the fluid interface in the target area.
2. The method as claimed in claim 1 wherein said two fluids are a gas and a liquid, said interface being a free surface of the liquid, the acoustic source and receiver being positioned above the liquid surface, the variations in phase shift being used indicate fluctuations over time in the height of the liquid surface.
3. The method as claimed in claim 2 wherein said liquid is flowing, the method further comprising deriving from the measured variations in phase shift a characteristic of the flowing liquid such as: surface roughness, wave height, flow depth, flow velocity, volumetric flow rate, shear stress, sediment transport.
4. The method as claimed in any preceding claim, wherein the sent acoustic signals comprise a harmonic sine wave and said processing step comprises comparing phases of the sent and received signals over several cycles of said sine wave to obtain a measurement of said phase shift at a given time.
5. The method as claimed in any preceding claim, wherein the phase shift is determined on the basis of Hilbert transforms of data representing the sent and detected acoustic signals.
6. The method as claimed in any preceding claim, further comprising:
arranging a plurality of acoustic receivers at different positions relative to the acoustic source so as to receive acoustic signals that have reflected from different target areas on the fluid interface and processing the received acoustic signals so as to measure a time-varying phase shift corresponding to each of said target areas.
7. The method as claimed in claim 6, wherein the plurality of acoustic receivers are spaced to allow different separation distances between different pairs of the receivers and hence different separation distances between different pairs of target areas.
8. The method of claim 6 or 7 wherein said acoustic receivers are spaced in two dimensions so that said different target areas are spaced in two dimensions over the fluid interface.
9. The method as claimed in claim 6, 7 or 8, further comprising measuring a temporal lag between fluctuations measured for different target areas.
10. The method as claimed in any preceding claim, further comprising:
determining a wave height at the target area on the basis of the measured variations in phase shift, a known separation of the acoustic source and receiver and a known receiver height relative to said interface.
11. The method as claimed in claim 10, wherein said known receiver height is obtained by measuring a time of flight of an acoustic signal sent from said acoustic source and received by said acoustic receiver following reflection from the interface.
12. An apparatus for use in measuring dynamic characteristics of an interface between two fluids, the apparatus comprising:
a signal emitter including an acoustic source operable to send acoustic signals from said acoustic source to at least one target area on the fluid interface;
a signal detector means including an acoustic receiver and operable to receive said acoustic signals using said acoustic receiver after reflection from the target area; and,
a signal processor operable to process the detected signals to measure phase shift between the sent and received acoustic signals, the measured phase shift varying over time, the variations in phase shift being usable to indicate fluctuations over time in the position of the fluid interface in the target area.
13. The apparatus as claimed in claim 12 adapted for use where said two fluids are a gas and a liquid, said interface being a free surface of the liquid, the acoustic source and receiver being adapted for placement above the liquid surface.
14. The apparatus as claimed in claim 13 wherein adapted for use where said liquid is flowing, the signal processor being further arranged to derive from the measured variations in phase shift a characteristic of the flowing including one or more of: surface roughness, wave height, flow depth, flow velocity, volumetric flow rate, shear stress, sediment transport.
15. The apparatus as claimed in claim, 12, 13 or 14, wherein the sent acoustic signals comprise a harmonic sine wave and wherein said processor is arranged to compare phases of the sent and received signals over several cycles of said sine wave to obtain a measurement of said phase shift at a given time.
16. The apparatus as claimed in any of claims 12 to 15, wherein the phase shift is determined on the basis of Hilbert transforms of data representing the sent and detected acoustic signals.
17. The apparatus as claimed in any of claims 12 to 16, wherein the signal emitter further comprises a plurality of acoustic receivers arranged at different positions relative to the acoustic source to receive acoustic signals that have reflected from different target areas on the fluid interface, and wherein the signal processor is operable to process the received acoustic signals so as to measure a time-varying phase shift corresponding to each of said target areas.
18. The apparatus as claimed in claim 17, wherein the pluraility of acoustic receivers are spaced to allow different separation distances between different pairs of the receivers, and hence different separation distances between different pairs of target areas.
19. The apparatus of claim 17 or 18 wherein said acoustic receivers are spaced in two dimensions so that in operation said different target areas will be spaced in two dimensions over the fluid interface.
20. The apparatus as claimed in claim 17, 18 or 19, wherein said signal processor is further operable to measure a temporal lag between fluctuations measured for different target areas.
21. The apparatus as claimed in any of claims 12 to 20, wherein the signal processor is further operable to determine a wave height at each point on the basis of the variations in phase shift, a known separation of the acoustic source and receiver and a known receiver height relative to said interface.
22. The apparatus as claimed in claim 15, wherein the processing module is further operable to obtain said known receiver height automatically by measuring a time of flight of an acoustic signal sent from said acoustic source and received by said acoustic receiver following reflection from the interface.
23. A processor arranged to receive data representing acoustic signals and to perform the processing step of any method as claimed in claims 1 to 11.
24. A computer-readable medium comprising instructions which when executed by a computer can perform the processing step of any method as claimed in claims 1 to 11.
PCT/GB2012/050489 2011-03-03 2012-03-05 Methods and apparatus for detection of fluid interface fluctuations WO2012117261A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US14/002,569 US20130333483A1 (en) 2011-03-03 2012-03-05 Methods and apparatus for detection of fluid interface fluctuations
EP12715702.2A EP2681520A1 (en) 2011-03-03 2012-03-05 Methods and apparatus for detection of fluid interface fluctuations

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB1103642.3A GB201103642D0 (en) 2011-03-03 2011-03-03 Methods and systems for detection of liquid surface fluctuations
GB1103642.3 2011-03-03

Publications (1)

Publication Number Publication Date
WO2012117261A1 true WO2012117261A1 (en) 2012-09-07

Family

ID=43904507

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2012/050489 WO2012117261A1 (en) 2011-03-03 2012-03-05 Methods and apparatus for detection of fluid interface fluctuations

Country Status (4)

Country Link
US (1) US20130333483A1 (en)
EP (1) EP2681520A1 (en)
GB (1) GB201103642D0 (en)
WO (1) WO2012117261A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016030077A1 (en) * 2014-08-26 2016-03-03 Endress+Hauser Gmbh+Co. Kg Method for avoiding phase jumps
CN110631957A (en) * 2019-08-30 2019-12-31 昆明理工大学 A device and method for detecting liquid level fluctuation characteristics based on acoustic signals
CN113884070A (en) * 2021-09-18 2022-01-04 华特数字科技有限公司 A measuring method based on intelligent flow measuring robot

Families Citing this family (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8600708B1 (en) 2009-06-01 2013-12-03 Paradigm Sciences Ltd. Systems and processes for building multiple equiprobable coherent geometrical models of the subsurface
US8743115B1 (en) 2009-10-23 2014-06-03 Paradigm Sciences Ltd. Systems and methods for coordinated editing of seismic data in dual model
EP2778725B1 (en) * 2013-03-15 2018-07-18 Emerson Paradigm Holding LLC Systems and methods to build sedimentary attributes
JP5905646B2 (en) * 2013-05-31 2016-04-20 三菱電機株式会社 Tsunami monitoring system
US9343898B2 (en) * 2013-07-19 2016-05-17 Texas Instruments Incorporated Driver current control apparatus and methods
GB2523094B (en) * 2014-02-12 2016-05-04 Jaguar Land Rover Ltd Vehicle water detection system
US9857460B2 (en) * 2014-12-19 2018-01-02 Mitsubishi Electric Corporation Waveform estimation device and waveform estimation method
US20160363471A1 (en) * 2015-06-09 2016-12-15 Andre Olivier Non-intrusive flow measurement and detection system
FI129728B (en) * 2016-06-27 2022-08-15 Flaekt Woods Ab Apparatus and method for measuring an air flow
US10466388B2 (en) 2016-09-07 2019-11-05 Emerson Paradigm Holding Llc System and method for editing geological models by switching between volume-based models and surface-based structural models augmented with stratigraphic fiber bundles
US10571315B2 (en) * 2017-09-21 2020-02-25 Hach Company Single-beam radar level and velocity sensing
CA3100117A1 (en) * 2018-06-07 2019-12-12 Wilco Ag Method and apparatus for monitoring a drive mechanism of an automated inspection system for inducing motion to a container partially filled with a liquid
US10520644B1 (en) 2019-01-10 2019-12-31 Emerson Paradigm Holding Llc Imaging a subsurface geological model at a past intermediate restoration time
US11156744B2 (en) 2019-01-10 2021-10-26 Emerson Paradigm Holding Llc Imaging a subsurface geological model at a past intermediate restoration time
CN112798221B (en) * 2020-12-07 2021-12-14 河海大学 Method for calculating starting shear stress of viscous silt bed surface based on agglomeration starting mechanism
DE102023000565A1 (en) * 2023-02-20 2024-08-22 Mercedes-Benz Group AG Method for determining a reception direction of a special acoustic signal

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3184969A (en) 1963-06-10 1965-05-25 Gen Signal Corp Liquid level indication system
FR2241080A1 (en) * 1973-08-14 1975-03-14 Commissariat Energie Atomique Acoustic measurement of liquid or powder surface level - by alteration of phase to produce standing wave
GB1600079A (en) 1976-02-18 1981-10-14 Redding R J Liquid level measuring
US4364264A (en) 1980-01-08 1982-12-21 Centro Ricerche Fiat S.P.A. Feeler device for measuring surface roughness
GB2121174A (en) * 1982-05-20 1983-12-14 Robert James Redding Measurement of distance using ultrasound
GB2188420A (en) 1986-03-25 1987-09-30 Atomic Energy Authority Uk Ultrasonic range finding
US5319974A (en) 1993-08-30 1994-06-14 Isco, Inc. Ultrasonic level measuring system
US20060037392A1 (en) 2004-08-17 2006-02-23 Steve Carkner Accoustical apparatus and method for measuring water level in a ground water well
WO2010020817A1 (en) * 2008-08-20 2010-02-25 University Of Bradford Improvements in and relating to apparatus for the airborne acoustic inspection of pipes
GB2472085A (en) 2009-07-24 2011-01-26 Wayne Rudd Methods and apparatus for determining the time of receipt of a received signal

Family Cites Families (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3921123A (en) * 1967-02-02 1975-11-18 Us Navy Torpedo target simulator
FR2064259A1 (en) * 1969-10-02 1971-07-23 Inst Francais Du Petrole
JP2640657B2 (en) * 1987-09-24 1997-08-13 株式会社日立メディコ Ultrasonic Doppler meter
US4821569A (en) * 1987-10-30 1989-04-18 Fischer & Porter Co. Parasitic echo pulse rejector for ultrasonic liquid level meter
WO1992002830A1 (en) * 1990-08-09 1992-02-20 Furuno Electric Company, Limited Underwater detecting device
FR2719669B1 (en) * 1994-05-03 1996-06-07 Thomson Csf Method and device for eliminating fixed echoes at intermediate frequency in a coherent pulse radar.
US5583301A (en) * 1994-11-09 1996-12-10 National Environmental Products Ltd., Inc. Ultrasound air velocity detector for HVAC ducts and method therefor
US5811688A (en) * 1996-01-18 1998-09-22 Marsh-Mcbirney, Inc. Open channel flowmeter utilizing surface velocity and lookdown level devices
US6307473B1 (en) * 1999-08-24 2001-10-23 Sensormatic Electronics Corporation Electronic article surveillance transmitter control using target range
DE60020724T2 (en) * 1999-09-24 2006-03-16 Japan Science And Technology Corp., Kawaguchi ULTRASONIC TRANSMITTER AND RECEIVER WITH PULSE COMPRESSION
EP1104093A1 (en) * 1999-11-24 2001-05-30 Telefonaktiebolaget Lm Ericsson Method and apparatus for generation of a RF signal
US20060100530A1 (en) * 2000-11-28 2006-05-11 Allez Physionix Limited Systems and methods for non-invasive detection and monitoring of cardiac and blood parameters
US6678617B2 (en) * 2001-06-13 2004-01-13 Nonlinear Seismic Imaging, Inc. Mapping subsurface open fractures using elastically nonlinear interaction of two surface-generated waves
US7254511B2 (en) * 2004-01-15 2007-08-07 Bae Systems Information And Electronic Systems Integration Inc. Method and apparatus for calibrating a frequency domain reflectometer
EP1851515B1 (en) * 2004-12-29 2019-04-24 Micro Motion Incorporated High speed frequency and phase estimation for flow meters
KR101337250B1 (en) * 2005-05-12 2013-12-06 컴퓨메딕스 메디컬 이노베이션 피티와이 엘티디 Ultrasound diagnosis and treatment apparatus
ATE483173T1 (en) * 2008-02-22 2010-10-15 Thales Nederland Bv METHOD FOR MEASURING THE RADIAL VELOCITY OF A TARGET USING A DOPPLER RADAR
CA2761580A1 (en) * 2008-05-13 2009-11-19 P. Square Medical Ltd. Monitoring conditions of a patient's urinary system

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3184969A (en) 1963-06-10 1965-05-25 Gen Signal Corp Liquid level indication system
FR2241080A1 (en) * 1973-08-14 1975-03-14 Commissariat Energie Atomique Acoustic measurement of liquid or powder surface level - by alteration of phase to produce standing wave
GB1600079A (en) 1976-02-18 1981-10-14 Redding R J Liquid level measuring
US4364264A (en) 1980-01-08 1982-12-21 Centro Ricerche Fiat S.P.A. Feeler device for measuring surface roughness
GB2121174A (en) * 1982-05-20 1983-12-14 Robert James Redding Measurement of distance using ultrasound
GB2188420A (en) 1986-03-25 1987-09-30 Atomic Energy Authority Uk Ultrasonic range finding
US5319974A (en) 1993-08-30 1994-06-14 Isco, Inc. Ultrasonic level measuring system
US20060037392A1 (en) 2004-08-17 2006-02-23 Steve Carkner Accoustical apparatus and method for measuring water level in a ground water well
WO2010020817A1 (en) * 2008-08-20 2010-02-25 University Of Bradford Improvements in and relating to apparatus for the airborne acoustic inspection of pipes
GB2472085A (en) 2009-07-24 2011-01-26 Wayne Rudd Methods and apparatus for determining the time of receipt of a received signal

Non-Patent Citations (7)

* Cited by examiner, † Cited by third party
Title
ANDREW NICHOLS ET AL.: "An airborne monochromatic acoustic method to measure the hydraulic characteristics of shallow water flows", JOURNAL OF ACCOUSTICAL SOCIETY OF AMERICA, vol. 128, no. 4, 1 October 2010 (2010-10-01), pages 2327 - 2327, XP002677639 *
COLEBROOK; WHITE: "Proceedings of the Royal Society of London", MATHEMATICAL AND PHYSICAL SCIENCES, vol. 161, no. 906, pages 367 - 381
E. I. THORSOS: "The validity of the Kirchhoff approximation for rough surface scattering using a Gaussian roughness spectrum", J. ACOUST. SOC. AM., vol. 83, no. 1, 1988, pages 78 - 92
LIU, H.-T.; K. B. KATSAROS; M. A. WEISSMAN: "Dynamic Response of Thin-Wire Wave Gauges", J. GEOPHYS. RES., vol. 87, no. C8, 1982, pages 5686 - 5698
NICHOLS, A. ET AL.: "Sonic Characterisation of Water Surface Waves", ISPF2010, NANJING, CHINA, 2010
See also references of EP2681520A1
YICHENG WANG ET AL: "NONCONTACT MONITORING OF LIQUID SURFACE LEVELS WITH A PRECISION OF 10 MICROMETERS: A SIMPLE ULTRASOUND DEVICE", REVIEW OF SCIENTIFIC INSTRUMENTS, AIP, MELVILLE, NY, US, vol. 62, no. 6, 1 June 1991 (1991-06-01), pages 1640 - 1641, XP000235659, ISSN: 0034-6748, DOI: 10.1063/1.1142445 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016030077A1 (en) * 2014-08-26 2016-03-03 Endress+Hauser Gmbh+Co. Kg Method for avoiding phase jumps
US10670705B2 (en) 2014-08-26 2020-06-02 Endress+Hauser Se+Co.Kg Method for avoiding phase jumps
CN110631957A (en) * 2019-08-30 2019-12-31 昆明理工大学 A device and method for detecting liquid level fluctuation characteristics based on acoustic signals
CN113884070A (en) * 2021-09-18 2022-01-04 华特数字科技有限公司 A measuring method based on intelligent flow measuring robot

Also Published As

Publication number Publication date
EP2681520A1 (en) 2014-01-08
US20130333483A1 (en) 2013-12-19
GB201103642D0 (en) 2011-04-13

Similar Documents

Publication Publication Date Title
US20130333483A1 (en) Methods and apparatus for detection of fluid interface fluctuations
Lemmin et al. Acoustic velocity profiler for laboratory and field studies
McLelland et al. A new method for evaluating errors in high‐frequency ADV measurements
CA2513248C (en) Apparatus and method using an array of ultrasonic sensors for determining the velocity of a fluid within a pipe
Franca et al. Eliminating velocity aliasing in acoustic Doppler velocity profiler data
Nystrom et al. Measurement of turbulence with acoustic doppler current profilers-sources of error and laboratory results
WO2013001503A3 (en) Method and apparatus for automated ultrasonic doppler angle and flow velocity estimation
Gunawan et al. ORNL ADCP post-processing guide and MATLAB algorithms for MHK site flow and turbulence analysis
Nichols et al. A non-invasive airborne wave monitor
NGUYEN et al. Development of multiwave method using ultrasonic pulse Doppler method for measuring two-phase flow
Krynkin et al. A non-invasive acoustical method to measure the mean roughness height of the free surface of a turbulent shallow water flow
WO2013017880A1 (en) Wear measurement
CN110440896B (en) Ultrasonic measurement system and measurement method
Mosquera et al. Salinity estimation from acoustic Doppler velocimeter measurements
Wada et al. Application of partial inversion pulse to ultrasonic time-domain correlation method to measure the flow rate in a pipe
JP4904099B2 (en) Pulse signal propagation time measurement device and ultrasonic flow measurement device
RU2584721C1 (en) Passive-active acoustic method of detection and localisation of gas leaks in gas-liquid medium
RU2545065C2 (en) Method to measure acoustic speed in water
RU2606205C1 (en) Pig-flaw detector
Biernacki et al. Non-invasive Ultrasound Doppler Effect Based Method of Liquid Flow Velocity Estimation in Pipe
Thang Two advanced non-intrusive methods for velocity distribution measurement in fluid mechanics with some recent research and development
Nichols et al. Low-cost 3D mapping of turbulent flow surfaces
Gazengel et al. Characterization of a loudspeaker free field radiation by laser doppler velocimetry
Pusppanathan Finite Element Analysis for Acoustic Wave Transmission in Ultrasonic Tomography Application
Murakawa et al. Higher flowrate measurement using ultrasonic pulsed Doppler method with staggered trigger

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 12715702

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: 2012715702

Country of ref document: EP

WWE Wipo information: entry into national phase

Ref document number: 14002569

Country of ref document: US

NENP Non-entry into the national phase

Ref country code: DE